Al-Qaeda's plot to blow up a US-bound plane with an underwear bomb is proof of
the "perverse and terrible" lengths they are willing to go,
according to Hillary Clinton.

The CIA on Monday announced it had disrupted an al-Qaeda plot to bring down a US-bound airline using a new underwear bomb around the anniversary of Osama bin Laden's death.

Terrorists in Yemen reportedly planned to use a device similar to the one that failed to explode on a plane to Detroit on Christmas Day in 2009 but American officials said the new bomb was significantly more sophisticated.

Early indications suggest the bomb may have been the work of Ibrahim al-Asiri, al-Qaeda's "master" bomb maker

While the would-be suicide bomber had yet to select a target and there was no imminent threat of attack, the plot served as a reminder of al-Qaeda's ambitions to strike against US civilians.

Leon Panetta, the US defence secretary, confirmed the operation, saying the US must "continue to remain vigilant against those that would seek to attack this country."

Mrs Clinton, the US Secretary of State, speaking in New Delhi, said: "It is a reminder as to why we have to remain vigilant at home and abroad in protecting our nation and in protecting friendly nations and peoples like India and others."

The FBI said it had recovered the explosive itself but it was not clear whether the terrorist had been captured or killed.

Last night, FBI technicians were analysing the device and early indications suggested it may have been the work of Ibrahim al-Asiri, al-Qaeda's "master" bomb maker.

The Saudi is believed to have made the bomb worn by Umar Farouk Abdulmutallab in his unsuccessful attempt to destroy a Northwest Airlines flight on Christmas 2009.

He is also thought to have been responsible for two bombs planted in print cartridges and put on US cargo planes in 2010. Both explosives were discovered and safely removed at East Midlands Airport in Leicestershire.

The latest bomb did not contain any metal elements and is likely to have passed unnoticed through a standard airport metal detector. However, it may been picked up by newer body scanners common at American airports.

"Initial exploitation indicates that the device is very similar to improvised explosive devices that have been used previously by al-Qaeda in the Arabian Peninsula in attempted terrorist attacks," the FBI said in a statement.

President Obama was first informed of the latest plot in April, raising questions as to why the US government had previously said there were no "specific or credible" terror threats linked to the May 2 anniversary of the al-Qaeda leader's death.